My go-to bag is the Petzl 30l bag (because I like to drag too many things around, apparently) with a 45l bag for bigger trips - the material is pretty tough (as long as the contents are padded); the clip-in point is fabric but seems very robust, and the bag keeps water out pretty well (no drain holes for me). The lid does get a bit destroyed in time but that doesn't actually really matter. I am wearing out the bottom of my older 45l bag slowly though - but they can be repaired (boat adhesive glue and PU-coated nylon patches; they aren't PVC). The waist strap on the 45l bag is also great when you can carry it on your back heavily loaded for walking caves or long walk-ins. You can get 200m+ of 9mm in one.
Two things are very annoying about the bag though...
1) for most dragging they are fine, but for dragging when full in rocky passages they always roll over so the off-centre attachment point is at the top and then they tend to dive into every obstruction... it should be possible to construct something to incorporate extra bits of cord or something to make it drag better by running them through the tightening cord holes.
2) (the really annoying one) for me, they wear through at the base of the shoulder straps where they are attached to the bag, and it is a bugger to fix (on the 30l you have to sew onto a patch and glue on, on the 45l it's very hard to fix). You never need to adjust down that far, so if you get some fat tubular webbing, and slide it over the straps and glue in place you can protect the connection from abrasion (you need to cut out a bit of the webbing where the strap attaches to the bag so it is covered).
also the fact that they are very expensive :O
For warm tropical caving though, the 45l bag is great
I have the 15l Petzl, which is nice, but I don't like the built-in donkey, erm, appendage - it's short and very thin. I'd rather have had a robust clip-in loop and use my own. It looks like the 22l bag has the same bit of cord?
Incidentally, all the Petzl bags are made without drain holes, and you can be free of the tyranny of drain holes if you ask someone (such as the sponsors of this forum) nicely. I assume you could also get Warmbac bags without the hole but they might need to be specially ordered or something?